The present invention generally pertains to bulk material analyzers and is particularly directed to an improved assembly of components for constructing a bulk material analyzer of the type that is used to analyze bulk material transported on a conveyor belt through an activation region located in a tunnel between at least one radiation source and at least one radiation detector within the bulk material analyzer.
Bulk material analyzers are used to measure the elemental content of bulk materials. In one type of bulk material analyzer, the radiation source includes one or more neutron sources and the radiation detector includes one or more gamma ray detectors that produce signals which are processed to provide a measurement of the elemental content of the bulk material. When the bulk material is bombarded with neutrons, emissions of gamma rays are produced from the bulk material. Different characteristic spectra of gamma ray energy are produced from different elements of the bulk material. By processing the detected signals that are indicative of the gamma ray spectrum a measurement is provided of the elemental content of the bulk material. This measurement process is known as prompt gamma ray neutron activation analysis (PGNAA). In addition to containing the radiation source and the radiation detector, the bulk material analyzer assembly necessarily includes a large quantity of radiation shielding material in order to protect persons using the bulk material analyzer from harmful doses of radiation. As used herein the term “radiation shielding material” means material that absorbs, scatters, attenuates and/or reflects neutron radiation and/or gamma radiation. The required quantity of radiation shielding material is such that some embodiments of the bulk material analyzer assembly are so large that the assembly is not easily handled for transportation from one site to another.
U.S. Pat. No. 5,396,071 to Atwell et al. describes a modular assembly for a PGNAA bulk material analyzer of the type in which bulk material is transported on a conveyor belt through an activation region located between at least one radiation source and at least one radiation detector within the bulk material analyzer. Such assembly includes container means that include a lower primary module containing radiation shielding material and defining either at least one radiation source cavity or at least one radiation detector cavity; and an upper primary module containing radiation shielding material and defining the other of either the at least one radiation source cavity or the at least one radiation detector cavity that is not defined by the lower primary module. The lower primary module and the upper primary module are so shaped that the passageway is delimited by placement of the upper primary module upon the lower primary module; and portions of the lower primary module are shaped for delimiting the sides of a trough that is contoured for accommodating passage of the conveyor belt through the activation region. The trough-delimiting portions of the lower module are inclined outwardly from the bottom of the passageway to accommodate a passage on a conveyor belt having a complementary contour.
The modular assembly described in the aforementioned U.S. Pat. No. 5,396,071 is easily handled for transportation and readily installed about a conveyor belt that is used for transporting the bulk material that is to be analyzed, such that the analyzer can be installed in an existing processing line without having to cut or otherwise disassemble the conveyor belt. As the so-described modular assembly has been applied to a wide range of applications, it has been found that a given embodiment thereof can be used with only small ranges of conveyor belt sizes and shapes. Although small differences in conveyor belt sizes and shapes have been compensated for by placing neutron-moderating-material liners of selected sizes and shapes on the respective modules adjacent the passageway, when such differences are not small it has been necessary to provide an entirely different bulk material analyzer assembly including a passageway and a trough having dimensions and shapes that are appropriate for accommodating the passage of the conveyor belt.
U.S. Pat. No. 6,157,034 to Griebel et al. describes a flexible modular assembly for a bulk material analyzer that can be modified for use with large ranges of conveyor belt sizes and shapes. The assembly includes a first module containing radiation shielding material and at least one radiation source; second module containing radiation shielding material and including at least one radiation detector; and at least two replaceable modules, each containing radiation shielding material, sandwiched between the first module and the second module to separate the first module from the second module, with the at least two replaceable modules being separated, to delimit a tunnel for movement of the bulk material through the activation region.
It is also known to install a PGNA bulk material analyzer by removing a section of an existing conveyor belt and conveyor support structure and installing the analyzer in the gap thus created in the conveyor support structure. This technique eliminates all conveyor belt support structural materials from the analysis volume and prevents extraneous signals from contaminating the analysis. However, use of this technique incurs considerable expenses in mechanical, civil and electrical engineering to redesign and rebuild the weakened conveyor support structure and to support the analyzer.